1. Field of the Invention
The present invention relates generally to building structures and, more particularly, to diaphragms used within building structures to form roofs capable of resisting deformation due to the imposition of horizontal sheer loads.
2. Description of the Prior Art
In the field of building construction, diaphragms are horizontal elements disposed at the floor and roof levels which provide vertical support and resist horizontal shear loads. The types of horizontal shear loads of particular concern are shear loads caused by earthquakes and/or high winds. Typically, variously configured metal decks are used to form diaphragms at the floor and roof levels of large commercial buildings.
The shear resistance offered by a diaphragm is dependant on a number of variables, such as the thickness of the metal deck, the span of the deck, and the manner of connecting the diaphragm to the supporting frame. Another factor which influences the shear resistance of the diaphragm is the degree of stiffness of the diaphragm, since a stiff diaphragm will reduce or limit the deflection of the building walls. If the stiffness of the diaphragm is increased, then the size of the diaphragm may also be increased, as the ultimate size of the diaphragm is a function of the degree of diaphragm deflection.
A number of types of metal decking products are known and are commercially available for constructing floor and roof decking of buildings. One such metal decking product is often referred to as fluted deck because each deck panel is corrugated or fluted to resist vertical deflection when bearing a load. Fluted deck is characterized by a number of alternating top and bottom flutes extending parallel to the longitudinal axis of the fluted deck panel. The top flutes lie substantially in an upper plane, and the bottom flutes lie substantially in a lower plane spaced apart from the upper plane. The alternating top and bottom flutes are interconnected by a series of webs extending parallel to the longitudinal axis of the fluted deck. Fluted deck is commercially available from a number of manufacturers, including Verco Manufacturing Company of Phoenix, Arizona, the assignee of the present application. Fluted deck is available in a variety of gauges (i.e., metal thickness), heights (i.e., the distance between the upper and lower flutes), widths, and lengths. Such fluted deck panels typically span between underlying horizontal load bearing members, such as horizontal support beams and are typically welded at their ends to the upper flange of the underlying support beams. The horizontal support beams are, in turn, supported by vertical load bearing members, such as vertical support beams.
Horizontal shear force is a measure of the force exerted upon one end of a diaphragm which tends to twist or rotate the diaphragm in a horizontal plane relative to the opposing end of the diaphragm. When sufficiently strong horizontal shear loads are imposed upon a diaphragm constructed of fluted deck panels, a number of failures tend to arise, including breaking of welds which secure the lower flutes to the underlying horizontal support beam, breaking of attachment points securing adjacent side edges of adjoining fluted deck panels, and buckling of the upper and lower flutes and interconnecting webs within the fluted deck panels. Investigations have been conducted to determine the specific points of failure resulting from the imposition of horizontal shear loads upon fluted deck. By destructive testing, it has been learned that presently used fluted decks, or variations thereof, tend to buckle and deform with little translation of the shear load forces to the underlying horizontal support beams, or to the vertical load bearing members which support such horizontal support beams.
Various structures have been developed in an attempt to create diaphragms which can resist high shear loads and which are relatively stiff. A representative type of such structure is described and illustrated in U.S. Pat. No. 3,759,006 to Tamboise. This patent discloses an open bay network diaphragm constructed form a plurality of longitudinally oriented frame members, each having a closed trapezoidal cross section. Segmented transversely oriented trapezoidal members extend intermediate adjacent longitudinally oriented frame members. Terminal flanges are connected along the outer sides of the frame members to create a modular-like unit for attachment to a building framework. Each such diaphragm is relatively stiff and able to absorb shear loads; however, such diaphragms are not rigidly attached to the supporting framework, but instead rest upon insulating wedges. Accordingly, little if any of the shear loads imposed upon such diaphragm is transferred to the supporting building framework.
U.S. Pat. No. 3,820,295 to Foley discloses a building structure formed of corrugated steel decking within both the vertical walls and the flooring. The corrugated floor panels are secured to the corrugated vertical walls by reinforcing strips which nest with the vertical wall panels. However, the disclosed structure is incapable of transferring significant horizontal shear forces imposed upon the horizontal diaphragm through any horizontal load bearing members to any vertical load bearing members capable of resisting such horizontal shear forces.
U.S. Pat. No. 3,720,029 to Curran discloses a fluted deck structure wherein the ends of the deck are sealed off be elements extending transverse to the direction of the flutes. The ends of each such deck panel are welded to an underlying horizontal support beam. However, the deck structure shown in this patent is designed to receive a concrete fill, and transfer of horizontal shear forces between the diaphragm and the underlying horizontal support beam is accomplished by shear transfer studs extending from the horizontal support beam and embedded within the concrete fill.
Other U.S. patents disclosing structures usable as decks or diaphragms for building include U.S. Pat. Nos. 583,685; 2,194,113; 2,485,165; 2,804,953; 3,483,663; 3,656,270; 3,973,366; 3,724,078; 3,956,864; 3,995,403.
Long span metal deck structures formed of individual inverted L-shaped elements are also known. Each long span deck element includes an upper horizontal flange and a vertical flange extending downwardly from one edge of the horizontal flange, terminating in an inverted T-shaped leg which rests upon an underlying horizontal support beam. Such long span decks are formed by interlocking a number of aforementioned deck elements to provide a continuous, relatively flat deck. It is known to construct such long span metal deck structures in the form of cantilevered configurations. For example, the November 1971 Long Span Metal decking brochure published by H. H. Robertson Co. of Pittsburgh, Pennsylvania shows a form of long span, or "LS" metal decking which may be used to form cantilevered deck structures. Profile plates are installed within the deck structure above the external horizontal support beam to stiffen the deck structure. At interior butt joints, a continuous T-shaped shear plate is welded to the top of the metal deck and to the underlying horizontal support beam; a separate cover plate is then installed above the butt joint and is welded to the top of the deck on both sides of the butt joint.
In U.S. Pat. No. 4,186,535 issued to the present applicant and assigned to the present assignee, a shear load resistant structure is disclosed wherein a Z-shaped or C-shaped load translation member is secured along an open end of a fluted deck to the top flutes of the deck and to an underlying external horizontal support beam to increase the shear resistance of the fluted deck. The load translation member precludes relative movement of the top and bottom flutes and transfers horizontal shear loads imposed upon the diaphragm to the underlying horizontal support beam. The shear resistant diaphragm structure disclosed in the patent has been marketed commercially by the present assignee under the trademark "SHEARTRANZ"; significant cost savings have been achieved through the use of "SHEARTRANZ" fluted deck structures by permitting the use of lighter gauge fluted deck panels in combination with heavier gauge load translation members to stiffen the deck and obtain equal or greater shear resistance values as would be obtained through the use of heavier gauge fluted deck panels alone.
In U.S. Pat. Nos. 4,333,280 and 4,335,557, also issued to the present applicant, a further load translation member is disclosed in the form of a profile plate member having a plurality of profile plate bent upwardly at a 90.degree. angle from a horizontal plate. The profile plates match the contour of the fluted deck and are welded to the webs and to the top flutes of the fluted deck along an open end thereof. The horizontal plate of the profile plate member is welded to the underlying horizontal support beam, as are the lower flutes of the fluted deck.
While the load translation members disclosed in the aforementioned U.S. Pat. Nos. 4,186,535; 4,333,280; and 4,335,557 all serve to increase the shear resistance of fluted deck diaphragms, the use of such load translation members imposes certain limitations upon the design of the diaphragms constructed therefrom. For example, each of the aforementioned Z-shaped, C-shaped and profile plate load translation members is adapted to be installed along an open end of the fluted deck, and is adapted to be welded to an underlying horizontal support beam. Thus, the use of such load translation members precludes the construction of cantilevered fluted deck structures wherein the open end of the fluted deck extends beyond and overhangs an external horizontal support beam.
Additionally, the Z-shaped and C-shaped load translation members shown in the aforementioned patents extend beyond the open end of the fluted deck and prevent the end of the fluted deck from fully extending to an adjacent vertical wall. While the profile plate member disclosed in U.S. Pat. Nos. 4,333,280 and 4,335,557 can be positioned to permit the end of the fluted deck to lie closely adjacent a vertical wall, the need to properly orient the profile plate member relative to the outer edge of the horizontal support beam, the need to properly orient the edge of the fluted deck relative to the profile plates, and the need to weld the profile plates to the ends of the webs and upper flutes, poses significant additional labor requirements for installation.
In large building structures, fluted deck panels are often placed end-to-end at internal horizontal support beams to form a continuous span; the end of one fluted deck panel is butted against the adjacent end of the next fluted deck panel, providing a so-called interior butt condition. As mentioned above, the Z-shaped and C-shaped load translation members disclosed in the aforementioned patent are designed to be installed along an open end of the fluted deck. Accordingly, such load translation members may not be installed along interior butt joints of a fluted deck diaphragm. While the profile plate members disclosed in the aforementioned U.S. Pat. Nos. 4,333,280 and 4,335,557 can be installed along interior butt joints, such profile plate members do not serve to join together the abutting ends of the respective fluted deck panels. Thus, while such a profile plate member may serve to stiffen one of the fluted deck panels, the abutting fluted deck panel is not simultaneously stiffened thereby. While a cover plate may be used to overlie the interior butt joint and join the upper flutes of the abutting fluted deck panels, the installation of such a cover plate requires additional welding steps, and increases the cost of construction.
Accordingly, it is an object of the present invention to provide a fluted deck diaphragm for use in a building structure and having a relatively high resistance to horizontal shear loads while using a less expensive, lighter gauge fluted deck panels.
It is another object of the present invention to provide such a fluted deck diaphragm wherein horizontal shear forces imposed upon the diaphragm are readily transferred to underlying horizontal load bearing members supported by vertical shear resisting load bearing members.
It is still another object of the present invention to provide such a fluted deck diaphragm having a cantilevered configuration.
It is yet another object of the present invention to provide such a fluted deck diaphragm including a shear resisting member interconnecting with the fluted deck and with the underlying horizontal support beam at a point spaced apart from the open end of the deck.
It is a further object of the present invention to provide such a fluted deck diaphragm wherein the open ends of the fluted deck lie directly adjacent a vertical exterior wall and incorporating a shear resistance member spaced apart from such vertical exterior wall.
It is a still further object of the present invention to provide such a fluted deck diaphragm incorporating a shear resisting member which may be easily installed at interior butt joints of the fluted deck for locking together the upper flutes of abutting fluted deck panels and transferring horizontal shear forces to the underlying horizontal support beam below the interior butt joint.
These and other objects of the present invention will become apparent to those skilled in the art as the description thereof proceeds.